Mice, immunized with an optimally immunogenic dose of Type III pneumococcal polysaccharide (SSS-III), were assayed at 2 hr. intervals for the presence of antibody-producing plaque-forming cells (PFC); the kinetic data obtained were compared to those for mice depleted of suppressor T cells by means of treatment with antilymphocyte serum. In both cases, the exponential increase in PFC proceeded in a stepwise fashion, and involved multiple non-random recruitment from a precursor cell population; however, additional stepwise increases in PFC occurred in mice depleted of suppressor T cells, resulting in a 20-fold increase in the magnitude of the PFC response. These results, in conjunction with the findings of previous studies, show that suppressor T cells act primarily by limiting the extent to which antibody-forming cells proliferate following immunization.